The present invention relates to means for preventing unrestricted, uncontrolled or inadvertent fluid flow that might otherwise occur as a result of loading or unloading fluid administration tubing sets in a medical pump. More particularly, the present invention relates to means for preventing unrestricted, uncontrolled or inadvertent “free flow” from a cassette, fluid administration set, or other fluid delivery device equipped with a movable flow stop as it is loaded into or removed from a medical pump.
Modern medical care often involves the use of medical pump devices to deliver fluids and/or fluid medicine to patients. Medical pumps permit the controlled delivery of fluids to a patient, and such pumps have largely replaced gravity flow systems, primarily due to the pump's much greater accuracy in delivery rates and dosages, and due to the possibility for flexible yet controlled delivery schedules. Of the modern medical pumps, those incorporating a diaphragm cassette are often preferred because they provide more accurately controlled rate and volume than do other types of pumps.
A typical positive displacement pump system includes a pump device driver and a fluid delivery device, including but not limited to a syringe, tubing, section of tubing, or a disposable cassette. The disposable cassette, which is adapted to be used only for a single patient and for a limited time, is typically a small plastic unit having an inlet and an outlet respectively connected through flexible tubing to a fluid supply container and to the patient receiving the fluid. The cassette includes a pumping chamber, with the flow of fluid through the chamber being controlled by a plunger activated in a controlled manner by the device driver against an elastomeric membrane or flexible diaphragm covering the pumping chamber.
Typically, when the cassette is loaded into the pump a normally closed flow stop on the cassette prevents the free flow of IV fluid either out of the pump onto the floor or improperly to a patient. This unintended, unrestricted, or uncontrolled flow problem is often described as “free flow.” Specifically, normally the pivotal flow stop of the cassette is closed and prevents such free flow until a cassette is properly installed in the pump and the cassette loader door is completely closed. At that point one side of the pivotal flow stop is operatively engaged by a pressure sensing distal pin in the pump. This leaves the flow stop in its normally closed position, but under the control of the pumping mechanism via the plunger and the passive outlet valve within the cassette. When the plunger pushes on the pumping chamber and sufficient pressure is generated therein, the outlet valve opens and allows fluid to flow. The pressure in the cassette just downstream from the outlet valve urges the flow stop pressure sensing distal pin upward as fluid is allowed to flow through the outlet of the cassette. Thus, once the cassette is properly installed in the pump, the pumping mechanism controls the opening and closing of the outlet valve and flow from the cassette.
Problems occur with the flow stop in a cassette when a cassette is mis-loaded or when a user prematurely pulls on the tubing upstream of the pump and yanks the cassette out of the pump before the cassette loader door is fully opened. As a result the flow stop can inadvertently come into contact with the distal pin, plunger or other components of the pumping mechanism or pump chassis, thereby causing the flow stop to be pivoted opened into a free flow position. Such free flow is undesirable.
Therefore, a first object of the present invention is to provide a fluid delivery device, such as a cassette or the like, for a medical pump having improved means for preventing free flow during installation and removal of the fluid delivery device.
Yet another object of the present invention is to provide enhanced means for preventing free flow that are simple and inexpensive to manufacture.
Yet another object of the present invention is to provide means on a cassette assembly that prevent pulling of the cassette assembly from a medical pump until the loader mechanism of the pump is fully open.
These and other objects will become apparent to those skilled in the art